1. Field of the Invention
The present invention relates to wireless networks, and particularly to a method of routing for wireless ad hoc and sensor networks defining a protocol based on the remaining energy of each wireless sensor node.
2. Description of the Related Art
A wireless ad hoc network (WANET) is a decentralized type of wireless network. The network is “ad hoc” because it does not rely on a pre-existing infrastructure, such as routers in wired networks or access points in managed (infrastructure) wireless networks. Rather, each node participates in routing by forwarding data for other nodes, so that the determination of which nodes forward data is made dynamically on the basis of network connectivity.
Routing in both WANETs and typical wireless sensor networks is typically governed by proactive routing, reactive routing, hybrid routing or position-based routing. Proactive routing protocols maintain fresh lists of destinations and their routes by periodically distributing routing tables throughout the network. Examples of such routing include the Optimized Link State Routing Protocol (OLSR) and distance vector routing. However, such proactive routing algorithms include the large amounts of data involved and the relatively slow reaction time for restructuring and failures. Additionally, although proactive routing protocols provide routes that are readily available when needed, energy consumption for sensor networks is excessive, since sensor devices have very limited energy sources (typically in the form of rechargeable batteries).
Reactive routing protocols find a route on demand by flooding the network with route request packets. Such flooding protocols, however, necessarily require a high latency time in route finding, and further, excessive flooding can lead to network clogging. A typical example of such a reactive routing protocol is the Ad hoc On-Demand Distance Vector (AODV) protocol. Hybrid routing protocols, such as the Zone Routing Protocol (ZRP), combine proactive and reactive routing schemes. The hybrid routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding. The choice of one or the other method requires predetermination for typical cases.
Position-based routing, such as Location-Aided Routing (LAR), requires the use of precise information on the exact locations of the nodes. This information is typically obtained via a global positioning system (GPS) receiver or the like, and can only be implemented when precisely accurate geographic information is possible for all nodes. Based on the exact locations, the best path between source and destination nodes can be determined.
The above typical routing protocols for WANETs and wireless sensor networks commonly suffer from problems with reliability. Most of the presently available routing algorithms attempt to find a desired route from the source to the destination before sending any data packets. Such protocols are susceptible to unreliable transmission when intermediate nodes are prone to change their configurations at regular intervals (i.e., changes in power, location, transmission mode, etc.
Additionally, the above typical routing protocols often suffer from degradation of performance when flawed sensor nodes intermittently arise. In order to minimize the effect of this issue, the portals try to explore alternate routes from the source or the faulty nodes to the destination for retransmission. However, this optimization problem is NP-complete, and the route information is unavailable for ad hoc networks. Thus, using one of the typical protocols for formulating a solution becomes an intrinsically complex problem.
Further, wireless sensor networks typically consist of a very large number of nodes. New nodes are likely to be added when necessary. It is much easier to maintain scalability in centralized wireless networks, such as cellular networks, because the scalability can be controlled centrally. However, ad hoc wireless networks do not have this capability, since the sensor nodes operate and collaborate in a cooperative manner. If any new node wants to join in the collaboration, it needs to be introduced with the whole network. Existing protocols, such as those described above, handle this issue by flooding the new node's information to its neighbor nodes, and it is propagated to every other node as well, in order to ensure scalability. This results in the flooding discussed above, and an additional problem of minimizing energy consumption while scaling the network.
Thus, a method of routing for wireless ad hoc and sensor networks addressing the aforementioned problems is desired.